The present invention relates to a coder/decoder for transmitting a television (TV) signal using a time compressed integration system and, more particularly, to a coder/decoder for a time compressed integration system, wherein the coder and decoder sections are arranged on a single IC chip and the coder/decoder is selectively used as a coder or decoder.
A time compressed integration (TCI) system is proposed as one of the TV signal transmission systems. In a TCI system, color video information is transmitted as a luminance signal (the Y signal) and two chrominance signals, i.e., a wide-band chrominance signal (to be referred to as a C.sub.W signal hereinafter) and a narrowband chrominance signal (to be referred to as a C.sub.N signal hereinafter). The TCI system utilizes the fact that the bands of the C.sub.W and C.sub.N signals require only about 1/4 the band of the Y signal when human visibility is taken into consideration. The C.sub.W and C.sub.N signals are time-compressed and are inserted in the horizontal flyback period of the TV signal, thereby transmitting the Y, C.sub.W, and C.sub.N signals after time compressed integration.
A TCI signal format will be described in detail with reference to FIGS. lA to lD. Image information picked up by a TV camera is extracted as R (red), G (green), and B (blue) signals, i.e., the primary color signals from the TV camera. The R, G, and B signals are converted into the Y, C.sub.W, and C.sub.N signals, as shown in FIGS. 1A, 1B, and 1C, respectively. The Y, C.sub.W, and C.sub.N signals are simultaneously input to a coder called a TCI coder and are converted into time compressed integration signals (TCI signals). In an image reproduced on a TV set, of 1H (one horizontal scanning period) signals, only signals of about 80% horizontal scanning period A excluding the horizontal flyback period are used in practice. In the TCI system, the signals in horizontal flyback period B are excluded from the Y, C.sub.W, and C.sub.N signals, and only signals in effective horizontal scanning period A are extracted. In a practical application of the TCI system, 1,536 luminance signal data as the Y signal, 384 wide-band chrominance signal as the C.sub.W signal, and 384 narrow-band chrominance signal as the C.sub.N signal are included as digital signals. The C.sub.W and C.sub.N signals within effective horizontal scanning period A are time-compressed and are inserted in horizontal flyback period B of the Y signal, thereby producing the TCI signal shown in FIG. 1D.
The initial bands of the C.sub.W and C.sub.N signals are about 1/4 the band of the Y signal. It is easy to time-compress these signals into those having the same band as that of the Y signal. Therefore, the TCI signal having a one-channel transmission band can be transmitted onto a transmission line. In the TCI system, the C.sub.W and C.sub.N signals are alternately extracted every 1H. In other words, the C.sub.W and C.sub.N signals are alternately inserted in horizontal flyback period B. Alternate insertion of the C.sub.W and C.sub.N signals every 1H in the TCI system is based on the following reason. In order to insert the C.sub.W and C.sub.N signals into horizontal flyback period B of the same 1H, horizontal flyback period B is not long enough. In order to insert all the C.sub.W, C.sub.N, and Y signals within the same 1H, even the Y signal must be time-compressed and the transmission band of the TCI signal is undesirably increased.
In the TCI system for inserting the C.sub.W and C.sub.N signals in each horizontal flyback period B in accordance with a line sequential scheme, the C.sub.W or C.sub.N signal is processed as if it is sampled at a 1/2 sampling rate of the horizontal scanning frequency in the vertical direction. The band of the TV signal in the vertical direction is a 1/2 frequency of the horizontal scanning frequency, i.e., (1/2).times.(Number of Lines Per Frame). For this reason, the band of the C.sub.W and C.sub.N signals in the vertical direction must be limited below 1/4 (the number of lines per frame) prior to time compression so as to prevent the folded component caused by sampling in the TCI coder from being mixed in the transmission band. A low-pass filter used for such band limitation is called a vertical filter.
FIG. 2 shows a general arrangement of a conventional TCI coder. The Y signal is input to selector 46 through first phase compensation delay circuit 41 serving as a FIFO (First-in First-out). The C.sub.W and C.sub.N signals are input to selector 44 through first and second vertical filters 42 and 43. Outputs from vertical filters 42 and 43 are alternately selected by selector 44 every 1H. The output from selector 44 is compressed by time compressor 45, and the compressed signal is input to selector 46. Selector 46 selects the Y signal from delay circuit 41 during effective horizontal scanning period A within 1H and the time-compressed C.sub.W or C.sub.N signal during horizontal flyback period B, and the selected signals are combined in accordance with time compressed integration, thereby generating the TCI signal, as shown in FIG. 1D. Delay circuit 41 compensates for the delay time of the C.sub.W and C.sub.N signals by vertical filters 42 and 43 and makes the phases of the C.sub.W and C.sub.N signals coincide with that of the Y signal. More specifically, vertical filters 42 and 43 comprise tapped delay devices each with a plurality of taps for generating delayed signals having different delay times in response to an input signal, logic circuits, i.e., a plurality of multipliers for multiplying the tap outputs with a given coefficient, and an adder for adding outputs from the multipliers. In this case, if each vertical filter 42 or 43 comprises a tapped delay device with seven taps (0H, 1H, 2H, 3H, 4H, 5H, and 6H) including the tap for zero delay time, the C.sub.W and C.sub.N signals are delayed by 3H from the Y signal. Therefore, delay circuit 41 must comprise a memory having a capacity corresponding to the 3H Y signal data.
The TCI signal output from the TCI decoder is transmitted from the sending end to the receiving end through a transmission medium (transmission line or recording medium). At the receiving end, the Y, C.sub.W, and C.sub.N signals are decoded by a decoder called a TCI decoder.
FIG. 3 shows a conventional arrangement of the TCI decoder. The Y signal component of the TCI signal is extracted as the Y signal output through second phase compensation delay circuit 51 as a FIFO memory. The C.sub.W and C.sub.N signal components are extracted as C.sub.W and C.sub.N signals through time compressor 52, interpolation filter 53, and selector 54. FIG. 4A shows the TCI signal transmitted to the receiving end, FIG. 4B shows the time-expanded C.sub.W and C.sub.N signals, and FIG. 4C shows the C.sub.W and C.sub.N signals interpolated by interpolation filter 53. FIGS. 4D to 4F show the Y, C.sub.W, and C.sub.N signals output from the TCI decoder.
As shown in FIG. 1D, the C.sub.W and C.sub.N signal components in the TCI signal fall within the range of the original horizontal scanning period and are transmitted after the corresponding Y signal. For this reason, in order to make the phases of the C.sub.W and C.sub.N signals coincide with that of the Y signal, the Y signal must be delayed by 1H.
The C.sub.W and C.sub.N signals are transmitted in accordance with the line sequential scheme. For example, during the horizontal scanning period in which only the C.sub.W signal is transmitted, the C.sub.N signal must be generated within the corresponding period in the receiving end. The C.sub.N signal is generated at the receiving end by using the C.sub.N signals in the preceding and succeeding horizontal scanning periods to interpolate the C.sub.N signal within the present horizontal scanning period. The C.sub.W signal must be generated within the period corresponding to the horizontal scanning period in which the C.sub.N signal is transmitted. This C.sub.W signal can be generated by the same interpolation scheme as in the C.sub.N signal. Interpolation is performed by interpolation filter 53. Filter 53 comprises a tapped delayed device and logic circuits (multipliers and an adder) in the same manner as in vertical filters 42 and 43. In this case, one of the C.sub.W and C.sub.N signals which is not to be interpolated is delayed by 1H in interpolation filter 53 so that it may be in phase with the other. The C.sub.W and C.sub.N signals alternately appear at the output of interpolation filter 53 in accordance with the odd- and even-numbered horizontal scanning periods. The C.sub.W and C.sub.N signals appear at the corresponding output terminals by the action of selector 54 which is switched every 1H.
The signal expanded by time expander 52 will be taken into consideration. Interpolation of the C.sub.W or C.sub.N signal in interpolation filter 53 during each horizontal scanning period is equivalent to the following operation. By using C.sub.W and C.sub.N signals which are 2H ahead of a given horizontal scanning period, the C.sub.W and C.sub.N signals which are 1H adhead of the given period are interpolated and generated. The above operation imposes an additional operation at the receiving end. That is, in addition to 1H delay of the Y signal so as to make the C.sub.W and C.sub.N signals coincide with the Y signal at the receiving end, the Y signal must be further delayed by 1H. Therefore, delay circuit 51 must comprise a memory having a capacity corresponding to the 2H Y signal data.
The C signals (representing the C.sub.W and C.sub.N signals) are delayed by 3H in the coder and 2H in the decoder with respect to the Y signal. The total delay time of the Y signal by delay circuits 41 and 51 is 5H (in the above description, delay circuits 41 and 51 perform 3H and 2H delay operations, respectively. However, in practice, a ratio of delay time of the delay circuit 41 to that of delay circuit 51 can be arbitrarily determined since a total delay time of 5H is required).
Generally speaking, assume that m-tapped (m taps) vertical filters 42 and 43 are used and n-tapped (n taps) interpolation filter 53 is used. The C signals are delayed by {(m-1)/2}H on the coder side and [{(n-1)/2}+1]H on the decoder side. The Y signal must be delayed by }(m+n)/2}H on the coder and decoder sides.
The TCI coder/decoder is often used in a system requiring both the coder and the decoder, such as a bidirectional TV transmission system, a recording/reproducing system (e.g. a VTR (Video Tape Recorder) and a video disc system). In such an application, it is desirable to mount the coder and decoder sections on a single LSI (Large Scale Integration) chip in order to reduce the number of circuit components. It is also desirable to selectively use it as a coder or decoder. If the coder and decoder which are shown in FIGS. 2 and 3 are mounted on a single LSI chip as independent circuits and are selectively used by a selector, the entire circuit size is greatly increased, and the number of elements constituting the circuit and the overall circuit area are increased. In particular, A memory (the 5H Y signal data which corresponds to the 20H C signal data) used for the phase compensation delay circuit for making the Y and C signals coincide with each other, a memory (the 12H C signal data) used as a delay device in the vertical filter, and a memory (the 2H C signal data) in the interpolation filter are required. The total capacity of these memory is large, which is a primary cause of a large circuit size. When the large coder/decoder is mounted on a single LSI chip, the yield and/or reliability of the LSIs is greatly degraded.